Serial data transmission is widely used for communication between devices. A serial communication interface frequently used is the so-called serial peripheral interface (SPI), which may for example be used in automotive applications for communication between nearby devices. For example, it may be used to retrieve sensor data. A very similar serial system is known under the name Microwire.
In conventional SPI systems, an SPI master supplies each of a plurality of SPI slaves with a clock signal. Based on this clock signal, also referred to as SPI clock, data communication between master and slaves is performed. Each slave may communicate with the master during assigned time slots.
The SPI clock signal toggles at the highest available data rate provided by the serial connection in such systems. Therefore, the SPI clock is a limiting signal regarding capacitive load and is furthermore a major contributor to electromagnetic emissions. An amount of slaves in such a system may be limited by a capacitive load on a clock line and/or by such emissions.
For example, in an automotive application increasing an amount of sensors which constitute slaves in a car may bring the serial peripheral interface to its data rate limit, as for each slave a time slot for transmission has to be assigned and therefore with a constant clock rate the data rate available per sensor may decrease with increasing number of sensors. On the other hand, increasing the clock rate may not be possible due to the above-explained effects.
While such constraints may be overcome by completely redesigning the communication system used, for example by using both edges of the clock signal for transmission of data or by dithering the clock signal, such approaches may for example require a significant modification of a master device used, which is undesirable in some circumstances. Also, a redesign of the communication system may be detrimental to backward compatibility with legacy devices, for example conventional SPI devices.